1. Field of the Invention
The present invention relates to multi-electrode pacing/sensing leads. More specifically, the invention relates to a new material utilized in electrode sleeves in an isodiametric multi-electrode pacing/sensing lead.
2. Description of the Prior Art
Heretofore, various materials have been proposed for use in the formation of electrode sleeves. Such materials have included stainless steel, elgiloy, platinum/irridium, tantalum or MP35N. All of these materials have exhibited properties required of such electrode sleeve material, such properties being ductility, radio-opacity and a desired degree of impedance to signal transmission to and from organic tissue.
Various methods of forming ring or sleeve electrodes have been proposed. Several examples of methods for forming and the sleeve electrodes formed thereby are disclosed in the following U.S. Patents:
______________________________________ U.S. Pat. No. PATENTEE ______________________________________ 3,942,536 Mirowski et al 3,664,347 Harmjanz 3,568,660 Crites 3,995,623 Blake et al 3,769,984 Muench 3,825,015 Berkovits 4,280,511 O'Neill ______________________________________
The Mirowski et al U.S. Pat. No. 3,942,536 discloses a cardioverting device having a single intravascular catheter wherein proximal and distal electrode assemblies on a catheter each comprise a plurality of spaced apart conductive metal rings. The rings are made of solid platinum irridium and are fitted snugly about a molded silicone rubber casing, with a spacing between the rings being provided to allow for flexibility of the electrode.
The Harmjanz U.S. Pat. No. 3,664,347 discloses an electric heart stimulation device wherein a filament or tubing of polyurethane is received over a plastic core. Between the filament and the core are two flexible wire conductors with portions of the filament cut away to expose the conductors at the desired locations. Sleeve electrodes can be slid over the tubing to contact the exposed conductors.
The Crites U.S. Pat. No. 3,568,660 discloses a pacemaker catheter which comprises a thin first layer of rubber over the exterior surface of a length of flexible tubing, and at least two electrical conductors helically wound over the surface of the tubing and embedded within the layer of rubber. An end portion of each conductor is then extracted from the rubber and wound around the tubing. Metal contact sleeves are then placed over the wound end portions to form spaced electrodes.
The Blake et al U.S. Pat. No. 3,995,623 discloses a catheter which is flow directed through the heart by a balloon on its distal end. The catheter preferably comprises two distal and three proximal electrodes, all of which are identical. Each electrode comprises a split collar of spring metal with the ends slidably overlapping. Each collar has an inner diameter slightly smaller than the outer diameter of the catheter over which they are positioned. Once the collars are relaxed, they grip the surface of the tube. The tube is softened by heating, allowing each collar to further contract into the body of the catheter to lock each electrode in a fixed position on the catheter. Each electrode is further sealed to the tube by annular deposits of adhesive.
The Muench U.S. Pat. No. 3,769,984 discloses a bipolar transverse pacing catheter with conductors therein formed of stranded tantalum which conductors are connected to respective electrodes by means of crimp rings. The crimp rings are also preferably formed of tantalum.
The Berkovits U.S. Pat. No. 3,825,015 discloses a single catheter that provides for separate electrical stimulation to the atrium or ventricle of a heart on mutually related conductors. The conductors within the catheter are welded to respective conductive rings, the rings being made from a platinum compound. The conductors themselves may be ordinary conductive copper wire or coiled wire. Means are provided for preventing electromagnetic interference between the atrial and ventricular stimulating conductors.
The O'Neill U.S. Pat. No. 4,280,511 discloses a multi-electrode lead assembly wherein an isodiametric multi-electrode assembly is formed by provision of a ring electrode of undisclosed material swaged into the lead insulation and wherein a soft metal such as silver is utilized between the ring electrode and a coiled wire core to provide electrical contact therebetween. A hole for the silver slug or ball is provided in a catheter wall.
Also, an isodiametric continuous non-split sleeve electrode received about and over a bared end of a wire conductor which is looped and knotted about a tubing in a pacing lead electrode assembly is disclosed in copending application Ser. No. 377,461 for: CARDIAC LEAD HAVING MULTIPLE RING ELECTRODES.
As will be described in greater detail hereinafter, the electrode sleeve of the present invention is fabricated from a rhenium/tungsten alloy and is crimped or swaged around a catheter in the area of the catheter where a conductor is brought from within the catheter through the catheter wall and wrapped in a coil around the exterior of the catheter. The electrode sleeve is swaged or crimped to compress the sleeve against the catheter wall thereby providing a uniform external diameter to the lead assembly then formed.
The rhenium/tungsten alloy material provides high ductility, radio-opacity and low impedance in signal transmission through living tissue.
Although the use of a rhenium/tungsten alloy per se as an electrodematerial has been proposed, the use of a rhenium/tungsten material in a medical implant has not heretofore been proposed.
Examples of rhenium/tungsten alloy electrodes used in other environments are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. PATENTEE ______________________________________ 1,877,261 Weiger 2,391,458 Hensel 3,307,198 Morgan 3,359,082 Dickinson et al 3,508,975 Osovitz et al 3,573,903 Delgrosso ______________________________________
The Weiger U.S. Pat. No. 1,877,261 discloses electrical make-and-break contacts for closing and opening electrical circuits with the contacts being formed from rhenium or an alloy containing rhenium, such as an alloy of rhenium and tungsten.
The Hensel U.S. Pat. No. 2,391,458 discloses metallic electrodes suitable for use in spark plugs, ignition systems, high frequency generators, high frequency induction furnaces, etc. The electrodes may be formed of various compositions, one of which is a rhenium plated rod having a core of tungsten, molybdenum or an alloy of tungsten and copper, or tungsten and silver.
The Morgan U.S. Pat. No. 3,307,198 discloses an electrode material for use in electrostatic recording heads comprising an alloy of tungsten and rhenium.
The Dickinson U.S. Pat. No. 3,359,082 and the Delgrosso U.S. Pat. No. 3,573,903 discloses various rhenium/tungsten alloys and methods for forming same.
The Osovitz et al U.S. Pat. No. 3,508,975 discloses a rhenium/tungsten alloy thermocouple with compensating lead wires.
As will be described in greater detail hereinafter the present invention differs from the various electrodes disclosed in the prior art patents listed above by providing a rhenium/tungsten electrode sleeve in an electrode assembly at the end of a pacing lead. Such an electrode sleeve has superior properties to ring electrodes presently in use in pacing lead electrode assemblies.